Hey and hello to Part 7 of the "Anatomy of a RC Crawler" by Sabaot. Lucky seven. Well, let it be lucky, as topic I'm refering in here is very important. Earlier we could laugh and say jokes. Now I must please that you all focus. Knowledge in here comes out of experience, not only theoretical research. Anyway, enjoy.
Right, as we are talking about power, lets say a thing or two about power sources. Say what you want, all will agree that
there is NEVER not enough power. Currently we are bound to batteries. And I don't talk about AA size, thes are suitable for Tx only.
I'm talking about RC batteries as a power supply. Currently we have two kinds of batteries available:
- NiHM (nickel-metal hydrate)
- LiPo (lithium-polymer)
At first - RC batteries are called "packs", "battery packs" because they consist of individual "batteries" connected into one
"pack" to get desired capacity and volt values. And lets explain these factors.
How to read that: NiMH 8.4v 7s 3,000 mAh ?
NiMH - nickel-metal hydrate
8.4v - power output
7s - seven cells (7 individual batteries, called cells, connected into one pack)
3,000 mAh (milliAmper hour) - power capacity; this particular pack can provide 3,000 mA (3A) of power during one hour.
These packs were commonly used in the past, now they are displaced by LiPo's. But still they are popular within RC Cars
and Trucks and they are widely available for Crawlers. And they aren't so good due to several factors:
- long charge times. Literally it takes hours to charge it fully and they require dedicated chargers. My 3,000 mAh according to charger info needs 8h of time to be fully charged (while giving max 20 mins of driving time).
- low charge power. Due to technology limitations NiMH must be charged with low power (more about that later) hence
long charge times, see above.
- memory effect. Mishandling NiMH can cause loss of capacity. This is common when NOT charging full, pack will
"remember" less than full charge and "set" it as new default. So you can make a 5,000 mAh pack into 3,000 mAh pack just
by wrong charging habit.
- purchase cost. Packs are expensive, especially the ones with greater capacity. Price is comparable to LiPo.
- quantity. If you want to provide yourself with some time of crawling you need a lot of packs so you can swap them as they are used. Long charging time forces you to have lots of packs or have long breaks between runs.
Charging a NiMH battery - long charging times comes out of the fact that power is given in small amount to prevent
overcharging the pack. NiMH is a chemical based battery and inside chemicals need time to accumulate and keep the
charge.
As for pluses, they are easy to assemble by yourself. Just buy enough individual cells, solder them into pack (schematics on the internet) and you are ready to go.
Now - LiPo's.
Name stands for Lithium-Polymer, technology commonly found in cell phones, laptops, and other mobile devices. The only
real difference between them and RC packs is discharge value - described as C factor. RC LiPo's have much higher
discharge rates than mobile devices.
Ok, so I have this:
1. LiPo, 2s1p, 30C, 5,200 mAh 8.4v charge rate 2C AND
2. LiPo 3s1p, 25-35C, 2,200 mAh 11.1v;
how to decipher that?
1.
LiPo - already known
2s1p - two cells connected in parallel
30C - discharge rate, how much power I can drain out of the pack without damaging it (more later)
5,200 mAh - total capacity in milliAmper hour
8.4v - volt value, depends on number of cells
2C charge - charge rate, how fast i can charge without damaging
2.
3s1p - three cells connected in parallel
25-35C - discharge rate, similar to above ex. but constant rate (25C) and peak rate (35C). It means that pack is designed for 25C discharge but can survive without any serious consequences short burtst of 35C.
11.1v - volt value
Now, that mysterious C factor.
I think it stand for "Capacity". A bit misleading tho as it is used with dis/charging rates. As a example we will use following
pack: 8.4v, 5,200 mAh 30C.
This means that our pack can provide 5.2A (5,200 mAh) over an hour time (8.4v is irrelevant at this time) - so it gives its
total capacity oven an hour - this is 1 times capacity = 1C.
But our pack has a 30C discharge factor. It means it can provide power 30 times its capacity = 156A of power! And mind
you that current of 0.1 - 0.2A is lethal! And our pack can give 780 times more current. Shocking. But mind also that our pack can do it at max and constant drain, which doesn't happen while crawling. in fact it doesn't happen at all. It's just
maximum hypotetical power output. Most of the time packs works at much lower output.
Ok, but how long our pack can provide that amounts of power, for an hour? No. The greater C factor, the shorter the time in which our pack will go empty. And it's reverse dependance:
@ 1C we have 5.2A/h
@ 2C we have 10.4A/half an h
...
@ 30C we have 156A/2 minutes !
So the more power you drain from your pack, the higher Ampers you can squeeze out but with a cost of shorter time of pack work. My experiments showed that 5,200 mAh can give anything between 20 mins and 1h, depending on how hard I'm driving my truck (fast Short Course 4x4, not a Crawler). One can equip its rig with a logger that measures power and draws a chart. In short - the harder the work the shorter the drive time.
Now charging.
Typically LiPo's are designed to be charged with 1C, so 2,200 mAh should be put under 2.2A, 5,200 mAh should be put
under 5.2A, and so on. This is how I charge my 11.1v 2,200 mAh packs. But my 8.4v 5,200 mAh has a 2C charge factor. So I can safely charge it with 10.4A (tho it's still recommended using 1C for longer life).
And similarily - if pack can provide 5.2A over an hour at 1C discharge rate, it can also acquire 5.2A over an hour at 1C
charge rate. At 2C charge we will finish charging after 30 minutes, 4C charging shotrens charge time to 15 minutes. There
are packs that allows charging values @ 5C! Tho they are insanely expensive. But with that all you need is just a 2 packs - in in model, 2nd charging. Before you run out of power your other pack will be long ready.
And so we have shown two major advantages of LiPo packs - high power output abilities and fast charge times. But to have that you need a specialised microprocessor charger. This is because of technology used in production of a pack.
Earlier I mentioned that volt value depend on cells count. Overall volt is a sum of volt values of particular cells inside the
pack. Single cell has 4.2v (1s1p - 1 cell in parallel to... well, itself) and various mAh value. If we connect two cells we get
8.4v (2s1p; 2x 4.2v); three cells are 11.1v, 4 cells = 16.8v, haven't seen 5s; 6s = 22.2v. In RC you can find even 12s packs. M-m-m-monster ones. Helicopters of class 600 and higher uses such a packs.
In other words, the more cells, the bigger volt value. Crawlers use NiMH around 5-9cell packs, LiPo's 2s (commonly), 3s -
I'm not sure, too much power I believe.
Now lets talk about that parallel. If pack can consist of parallel cells, can it have in series? The answer is (maybe a bit
indirect): pack can be connected with each other either in parallel, or in series. The result of that connection depend on a
connection method.
Parallel - used to sum up capacity, having volt and mAh the same.
11.1v 2,200 mAh + 11.1v 2,200 mAh = 11.1v 4,400 mAh.
I'm not sure what happens with C factor, does it sums as well or remains. Clarification needed.
In series - used to sum up volt and mAh, having capacity unaltered.
11.1v 2,200 mAh + 11.1v 2,200 mAh = 22.2v 2,200 mAh.
Same applies to individual cells. If you have several packs and all have bad some cells you can deconstruct them to reclaim good cells and solder the good cells into desired new pack.
Note: we ONLY connect packs with the same specification. So two 11.1v 2,200 mAh are fine but 11.1v 2,200 mAh and 7.4v 5,200 mAh is a bad idea.
Ok, all super extra, now there's time for drawbacks. As usual.
First and foremost - RC LiPo's are dangerous stuff. Property damage, fire hazard, serious injury or even death can occur
while poor handling and not following safety issues.
RC LiPo's - bare that in mind, tattoo on a forehead if necessary to NEVER forget - are extremely flammable and DOESN'T like being punctured, overcharged, too deeply discharged, heated. Treat them like that and it's the fastest way to cause a fire or even an explosion. Don't believe me? Seek "lipo fire" and/or "lipo explosion" on YT.
In case you are new to LiPo's, or somehow forgot how to handle them, I provide PROPER and SAFE volt values:
charged pack - 4.20v per cell
discharged pack - 3.60v per cell
Anything OVER (charged) or BELOW (discharged) these values can lead to battery malfunction, shorter life span and in
extreme situations - disaster.
And how to figure those values. First you need microprocessor charger designed for charging LiPo's. Good starting item is
(announcement: this article includes product placement) Turnigy Accucell 6. Perfect for a start, good quality for money,
accepts various NiMH (2-15s I believe) and LiPo's 2-6s, 50W power, 6A max charge, various cables for connection.
Requires 12v input power source (you can buy dedicated one or mod a X-Box power supply unit/ use laptop PSU).
Why I'm taking about charger - main reason is it has built in a balancer. What's that you ask - it's a special circuit that
ensures all the cells within the pack are charged evenly. Normal charger fills pack with energy as it pleases. It puts 2,200
mAh into 3s 11.1v pack. Fine you say. But measuring voltage on particular cells you can see following:
3.89 / 4,47 / 4,24.
This means that 1st cell is undercharged, 2nd is heavily overcharged, 3rd is slightly (within safety margin) overcharged.
This will cause that when using that pack 1st cell will drop quicky far below safety of 3.60v and 2nd cell, due to heavy
overcharge, will lost its lifespan. Overall entire pack will quickly "erode" and loose its functionality.
Now, microprocessor charger with balancer (provided you are using proper program) sees that you plugged discharged
pack and then charges all three cells evenly. If one cell reaches higher volt value, charger redirests power toward other two and rises their volts to match equality. And it stops charging all cells after reaching 4.20v.
As a final word. Mishandled LiPo's at first will "puff". New and healthy pack (not a hardcase) is hard and stiff in touch.
When it starts to show first signs of wear it will probably puff - slightly increase its volume, edges become rounded and you will feel soft spots when pressed. It feels like someone put a small ballon underneath. Those packs are still usable but
require extra care and observation. Better dispose (in a proper way) half good pack and buy a new one than watching how your entire model burns down.
Also - DO NOT leave LiPo packs fully charged / discharged for a long period of times (few months, let's say 4+), they don't
like it and may puff. For storaging use "storage" charging program on your charger. This will charge packs to 3.80-3.90v per cell level - a safety value for storaging LiPo's for a longer time.
Woot, some great article it became. I have problems with K.I.S.S. in my case it's rather K.I.L.L (keep it large nad long).
Anyway, all starting with RC should have now a very basic knowledge about power sources. rest will come with time and
experience.
Happy Crawling. And don't forget to visit Part 8 of the "Anatomy of a RC Crawler" by Sabaot. I'd cry if all my writing and
time spent were wasted if noones is interested.
Right, as we are talking about power, lets say a thing or two about power sources. Say what you want, all will agree that
there is NEVER not enough power. Currently we are bound to batteries. And I don't talk about AA size, thes are suitable for Tx only.
I'm talking about RC batteries as a power supply. Currently we have two kinds of batteries available:
- NiHM (nickel-metal hydrate)
- LiPo (lithium-polymer)
At first - RC batteries are called "packs", "battery packs" because they consist of individual "batteries" connected into one
"pack" to get desired capacity and volt values. And lets explain these factors.
How to read that: NiMH 8.4v 7s 3,000 mAh ?
NiMH - nickel-metal hydrate
8.4v - power output
7s - seven cells (7 individual batteries, called cells, connected into one pack)
3,000 mAh (milliAmper hour) - power capacity; this particular pack can provide 3,000 mA (3A) of power during one hour.
These packs were commonly used in the past, now they are displaced by LiPo's. But still they are popular within RC Cars
and Trucks and they are widely available for Crawlers. And they aren't so good due to several factors:
- long charge times. Literally it takes hours to charge it fully and they require dedicated chargers. My 3,000 mAh according to charger info needs 8h of time to be fully charged (while giving max 20 mins of driving time).
- low charge power. Due to technology limitations NiMH must be charged with low power (more about that later) hence
long charge times, see above.
- memory effect. Mishandling NiMH can cause loss of capacity. This is common when NOT charging full, pack will
"remember" less than full charge and "set" it as new default. So you can make a 5,000 mAh pack into 3,000 mAh pack just
by wrong charging habit.
- purchase cost. Packs are expensive, especially the ones with greater capacity. Price is comparable to LiPo.
- quantity. If you want to provide yourself with some time of crawling you need a lot of packs so you can swap them as they are used. Long charging time forces you to have lots of packs or have long breaks between runs.
Charging a NiMH battery - long charging times comes out of the fact that power is given in small amount to prevent
overcharging the pack. NiMH is a chemical based battery and inside chemicals need time to accumulate and keep the
charge.
As for pluses, they are easy to assemble by yourself. Just buy enough individual cells, solder them into pack (schematics on the internet) and you are ready to go.
Now - LiPo's.
Name stands for Lithium-Polymer, technology commonly found in cell phones, laptops, and other mobile devices. The only
real difference between them and RC packs is discharge value - described as C factor. RC LiPo's have much higher
discharge rates than mobile devices.
Ok, so I have this:
1. LiPo, 2s1p, 30C, 5,200 mAh 8.4v charge rate 2C AND
2. LiPo 3s1p, 25-35C, 2,200 mAh 11.1v;
how to decipher that?
1.
LiPo - already known
2s1p - two cells connected in parallel
30C - discharge rate, how much power I can drain out of the pack without damaging it (more later)
5,200 mAh - total capacity in milliAmper hour
8.4v - volt value, depends on number of cells
2C charge - charge rate, how fast i can charge without damaging
2.
3s1p - three cells connected in parallel
25-35C - discharge rate, similar to above ex. but constant rate (25C) and peak rate (35C). It means that pack is designed for 25C discharge but can survive without any serious consequences short burtst of 35C.
11.1v - volt value
Now, that mysterious C factor.
I think it stand for "Capacity". A bit misleading tho as it is used with dis/charging rates. As a example we will use following
pack: 8.4v, 5,200 mAh 30C.
This means that our pack can provide 5.2A (5,200 mAh) over an hour time (8.4v is irrelevant at this time) - so it gives its
total capacity oven an hour - this is 1 times capacity = 1C.
But our pack has a 30C discharge factor. It means it can provide power 30 times its capacity = 156A of power! And mind
you that current of 0.1 - 0.2A is lethal! And our pack can give 780 times more current. Shocking. But mind also that our pack can do it at max and constant drain, which doesn't happen while crawling. in fact it doesn't happen at all. It's just
maximum hypotetical power output. Most of the time packs works at much lower output.
Ok, but how long our pack can provide that amounts of power, for an hour? No. The greater C factor, the shorter the time in which our pack will go empty. And it's reverse dependance:
@ 1C we have 5.2A/h
@ 2C we have 10.4A/half an h
...
@ 30C we have 156A/2 minutes !
So the more power you drain from your pack, the higher Ampers you can squeeze out but with a cost of shorter time of pack work. My experiments showed that 5,200 mAh can give anything between 20 mins and 1h, depending on how hard I'm driving my truck (fast Short Course 4x4, not a Crawler). One can equip its rig with a logger that measures power and draws a chart. In short - the harder the work the shorter the drive time.
Now charging.
Typically LiPo's are designed to be charged with 1C, so 2,200 mAh should be put under 2.2A, 5,200 mAh should be put
under 5.2A, and so on. This is how I charge my 11.1v 2,200 mAh packs. But my 8.4v 5,200 mAh has a 2C charge factor. So I can safely charge it with 10.4A (tho it's still recommended using 1C for longer life).
And similarily - if pack can provide 5.2A over an hour at 1C discharge rate, it can also acquire 5.2A over an hour at 1C
charge rate. At 2C charge we will finish charging after 30 minutes, 4C charging shotrens charge time to 15 minutes. There
are packs that allows charging values @ 5C! Tho they are insanely expensive. But with that all you need is just a 2 packs - in in model, 2nd charging. Before you run out of power your other pack will be long ready.
And so we have shown two major advantages of LiPo packs - high power output abilities and fast charge times. But to have that you need a specialised microprocessor charger. This is because of technology used in production of a pack.
Earlier I mentioned that volt value depend on cells count. Overall volt is a sum of volt values of particular cells inside the
pack. Single cell has 4.2v (1s1p - 1 cell in parallel to... well, itself) and various mAh value. If we connect two cells we get
8.4v (2s1p; 2x 4.2v); three cells are 11.1v, 4 cells = 16.8v, haven't seen 5s; 6s = 22.2v. In RC you can find even 12s packs. M-m-m-monster ones. Helicopters of class 600 and higher uses such a packs.
In other words, the more cells, the bigger volt value. Crawlers use NiMH around 5-9cell packs, LiPo's 2s (commonly), 3s -
I'm not sure, too much power I believe.
Now lets talk about that parallel. If pack can consist of parallel cells, can it have in series? The answer is (maybe a bit
indirect): pack can be connected with each other either in parallel, or in series. The result of that connection depend on a
connection method.
Parallel - used to sum up capacity, having volt and mAh the same.
11.1v 2,200 mAh + 11.1v 2,200 mAh = 11.1v 4,400 mAh.
I'm not sure what happens with C factor, does it sums as well or remains. Clarification needed.
In series - used to sum up volt and mAh, having capacity unaltered.
11.1v 2,200 mAh + 11.1v 2,200 mAh = 22.2v 2,200 mAh.
Same applies to individual cells. If you have several packs and all have bad some cells you can deconstruct them to reclaim good cells and solder the good cells into desired new pack.
Note: we ONLY connect packs with the same specification. So two 11.1v 2,200 mAh are fine but 11.1v 2,200 mAh and 7.4v 5,200 mAh is a bad idea.
Ok, all super extra, now there's time for drawbacks. As usual.
First and foremost - RC LiPo's are dangerous stuff. Property damage, fire hazard, serious injury or even death can occur
while poor handling and not following safety issues.
RC LiPo's - bare that in mind, tattoo on a forehead if necessary to NEVER forget - are extremely flammable and DOESN'T like being punctured, overcharged, too deeply discharged, heated. Treat them like that and it's the fastest way to cause a fire or even an explosion. Don't believe me? Seek "lipo fire" and/or "lipo explosion" on YT.
In case you are new to LiPo's, or somehow forgot how to handle them, I provide PROPER and SAFE volt values:
charged pack - 4.20v per cell
discharged pack - 3.60v per cell
Anything OVER (charged) or BELOW (discharged) these values can lead to battery malfunction, shorter life span and in
extreme situations - disaster.
And how to figure those values. First you need microprocessor charger designed for charging LiPo's. Good starting item is
(announcement: this article includes product placement) Turnigy Accucell 6. Perfect for a start, good quality for money,
accepts various NiMH (2-15s I believe) and LiPo's 2-6s, 50W power, 6A max charge, various cables for connection.
Requires 12v input power source (you can buy dedicated one or mod a X-Box power supply unit/ use laptop PSU).
Why I'm taking about charger - main reason is it has built in a balancer. What's that you ask - it's a special circuit that
ensures all the cells within the pack are charged evenly. Normal charger fills pack with energy as it pleases. It puts 2,200
mAh into 3s 11.1v pack. Fine you say. But measuring voltage on particular cells you can see following:
3.89 / 4,47 / 4,24.
This means that 1st cell is undercharged, 2nd is heavily overcharged, 3rd is slightly (within safety margin) overcharged.
This will cause that when using that pack 1st cell will drop quicky far below safety of 3.60v and 2nd cell, due to heavy
overcharge, will lost its lifespan. Overall entire pack will quickly "erode" and loose its functionality.
Now, microprocessor charger with balancer (provided you are using proper program) sees that you plugged discharged
pack and then charges all three cells evenly. If one cell reaches higher volt value, charger redirests power toward other two and rises their volts to match equality. And it stops charging all cells after reaching 4.20v.
As a final word. Mishandled LiPo's at first will "puff". New and healthy pack (not a hardcase) is hard and stiff in touch.
When it starts to show first signs of wear it will probably puff - slightly increase its volume, edges become rounded and you will feel soft spots when pressed. It feels like someone put a small ballon underneath. Those packs are still usable but
require extra care and observation. Better dispose (in a proper way) half good pack and buy a new one than watching how your entire model burns down.
Also - DO NOT leave LiPo packs fully charged / discharged for a long period of times (few months, let's say 4+), they don't
like it and may puff. For storaging use "storage" charging program on your charger. This will charge packs to 3.80-3.90v per cell level - a safety value for storaging LiPo's for a longer time.
Woot, some great article it became. I have problems with K.I.S.S. in my case it's rather K.I.L.L (keep it large nad long).
Anyway, all starting with RC should have now a very basic knowledge about power sources. rest will come with time and
experience.
Happy Crawling. And don't forget to visit Part 8 of the "Anatomy of a RC Crawler" by Sabaot. I'd cry if all my writing and
time spent were wasted if noones is interested.
